Method of Fabricating Optical Fiber

ABSTRACT

A method of making an optical fiber article can include providing an optical fiber including at least a core; providing a preform; and subsequent to the foregoing providing of the optical fiber and the preform, drawing the preform so as to dispose a region about the optical fiber. An optical fiber article can include a core; a pump cladding disposed about the core, the pump cladding for propagating pump light; and a second cladding disposed about the pump cladding, where the second cladding can provide a photonic bandgap for tending to confine pump light to a region about which the second cladding is disposed. The second cladding can comprise a plurality of layers including a first layer having a different optical property than a second layer, and the plurality of layers can be arranged as to provide the photonic bandgap effect.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of application Ser. No.11/178,011, filed Jul. 8, 2005 and entitled “Optical Fiber Article andMethods of Making”. The foregoing application is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to waveguides for propagating or guidingelectromagnetic energy, such as, for example, optical fibers, andmethods of making such waveguides.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a method of making anoptical fiber article. The method can comprise providing an opticalfiber comprising at least a core; providing a preform; and subsequent tothe foregoing providing of the optical fiber and the preform, drawingthe preform so as to dispose a region about the optical fiber. Thepreform can comprise a first polymer, and the first polymer can comprisea polyimide. The region can comprise a second polymer. The secondpolymer can be different than the first polymer, or the second polymercan be substantially identical to the first polymer. The preform cancomprise a metal. The preform can comprise a first metal and a firstpolymer and the region can comprise a second metal and a second polymer.The first and second metals can be different or substantially identical,and/or the first and second polymers can be different or substantiallyidentical. The preform can define an aperture and drawing the preformcan comprise passing the optical fiber through the aperture.

Providing the preform can comprise providing a sheet material. The sheetmaterial can be formed into a tube. Providing the preform can comprisefusing adjacent portions of the tube together. The tube can comprise aspiral of the sheet material. The sheet material can comprise a layer ofa first material adhered to a layer of a second material that isdifferent than the first material. The first material can comprise ametal and the second material can comprise a polymer. Providing thefiber can comprise drawing the fiber from an optical fiber preform.Drawing the fiber and drawing the preform to dispose the region aboutthe optical fiber can occur substantially contemporaneously. Providingthe optical fiber can include refraining from disposing a polymerprotective region about the optical fiber. The method can compriseproviding an adhesion promoter while drawing the preform for promotingadhesion of the region to the fiber. The adhesion promoter can comprisea silane.

In another aspect, the invention provides an optical fiber articlehaving a longitudinal axis, the optical fiber article comprising a corefor propagating light having a first wavelength; a pump claddingdisposed about the core and for propagating pump light including awavelength different than the first wavelength, where the pump claddingtends to confine light having the first wavelength to the core but doesnot tend to so confine the light having the first wavelength via aphotonic bandgap effect; and a second cladding disposed about the pumpcladding, where the second cladding provides a selected photonic bandgapfor tending to confine pump light within a region about which the secondcladding is disposed. The second cladding can be adjacent the pumpcladding and the region to which the second cladding tends to confinepump light can comprise the pump cladding.

The optical fiber article can comprise a rare earth. The rare earth cancomprise ytterbium. The pump cladding can be substantially homogeneous.The pump cladding can comprise a plurality of isolated features eachhaving an optical property (e.g., an index of refraction) that isdifferent than an optical property of material adjacent the features forproviding the pump cladding with a selected geometric refractive index.The second cladding can comprise a plurality of isolated features eachhaving an optical property (e.g., an index of refraction) that isdifferent than material adjacent the features. The plurality of isolatedfeatures of one or both of the inner and second claddings can comprise aplurality of longitudinally extending voids.

The second cladding can comprise a plurality of layers including a firstlayer having a different optical property (e.g., index of refraction)than a second layer. The first layer can have an index of refractionthat is higher than an index of refraction of the second layer. Theplurality of layers can comprise at least a first layer that forms aspiral about the longitudinal axis. The plurality of layers can comprisea plurality of concentric closed rings. The optical fiber article cancomprise an additional cladding disposed about the pump cladding, wherethe second cladding is disposed about the additional cladding and theadditional cladding comprises an effective index of refraction that isless than the effective index of refraction of the pump cladding. Theadditional cladding can comprise a plurality of isolated features eachhaving an index of refraction that is different than material adjacentthe feature for providing the additional cladding with a selectedgeometric refractive index for tending to confine pump light to the pumpcladding. The plurality of isolated features can comprise a plurality oflongitudinally extending voids.

In yet an additional aspect, the invention provides an optical fiberarticle having a longitudinal axis, where the optical fiber articlecomprises a core; a pump cladding disposed about the core, where thepump cladding is for propagating pump light; and a second claddingdisposed about the pump cladding, where the second cladding comprises aplurality of layers including a first layer having a different opticalproperty than a second layer, and the plurality of layers are arrangedso as to provide a photonic bandgap for tending to confine pump light toa region about which the second cladding is disposed. The first layercan have a higher index of refraction than the second layer. The opticalfiber article can comprise a rare earth, which rare earth can compriseytterbium. The plurality of layers can include at least a first layerthat forms a spiral about the longitudinal axis. The plurality of layerscan comprise a plurality of concentric closed rings. The optical fiberarticle can comprise an additional cladding disposed about the pumpcladding, where the second cladding is disposed about the additionalcladding, and the additional cladding comprises an effective index ofrefraction that is less than the effective index of refraction of thepump cladding. The additional cladding can comprise a plurality ofisolated features each having an index of refraction that is differentthan material adjacent the feature for providing the additional claddingwith a selected geometric refractive index for tending to confine pumplight to the pump cladding.

The plurality of isolated features can comprise a plurality oflongitudinally extending voids. The pump cladding can comprise aplurality of isolated features each having an index of refraction thatis different than the index of refraction of material adjacent thefeature. The plurality of isolated features contribute to providing aselected geometrical index of refraction for tending to confine light tothe core, or can contribute to providing a selected photonic bandgap.The pump cladding can provide a selected photonic bandgap for tending toconfine light to the core. The plurality of isolated features cancomprise a plurality of longitudinally extending voids. The pumpcladding can be substantially homogeneous.

It can be useful to comment on the distinction between the terms“refractive index”; “geometrical index”; and “effective index” as wellas on the various technical mechanisms by which different types of fiberare understood to operate (without wishing to be bound by theory unlessa mechanism of operation is expressly recited in the appended claims).The term “refractive index” (or “index of refraction”) refers to theconventional refractive index of a material, such as, for example, asubstantially homogeneous material (e.g., undoped or suitably dopedsilica glass). Most, if not all, materials can be characterized by arefractive index that can at least be estimated or at least determinedto be different than another index of refraction. For example, thewell-known Fresnel equations can provide an estimate of refractive indexbased reflection of light traveling in a medium of known refractiveindex (e.g., air) that reflects at normal incidence from another regionwhose refractive index is to be characterized. Metals are considered tohave an index of refraction. Stating herein that a region includes anindex of refraction does not mean that the index of refraction need beconstant throughout the region. For example, the core of a conventionalgraded index fiber can include an index of refraction that is greaterthan an index of refraction of a cladding surrounding the core, but theindex of refraction of the graded index core is not constant, as is wellunderstood by one of ordinary skill in the art.

The geometrical index of a structure is the geometrical weighted indexof the structure. Consider, for example, a structure consisting of avolume fraction of 40% air (refractive index of 1) and a volume fractionof 60% silica (refractive index of approximately 1.45). Such a structurehas a geometrical refractive index of (0.4×1)+(0.6×1.45), which is 1.27.If such a structure is used as a cladding of, for example, an undopedsilica core, the structure can in certain useful circumstances beconsidered to act on a macroscopic scale as having an index determinedlargely by the considerations of the geometrical index.

The effective refractive index, sometimes referred to as effectiveindex, of a given structure for a selected wavelength or range ofwavelengths is well known in the art. See, for example, Joannopoulos etal., “Photonic Crystals”, Princeton University Press, 1995. See also,Broeng et al., Optical Fiber Technology, Vol. 5, pp. 305-330, 1999. Anumerical method capable of solving Maxwell's equations in fullvectorial form can be used for accurate determination of the effectiveindices of refraction of complex structures including photonic bandgapstructures, where a region can include features that provide a selectedBragg condition or that provide for selected scattering. The foregoingJoannopoulos method is well documented in the literature. For certainstructures and operating conditions (e.g., operating wavelengths), theeffective index is roughly identical to the weighted average of theconstituents of a region, that is, the effective index is roughlyidentical to the geometrical index. The effective refractive index canalso be, in certain circumstances, substantially identical to therefractive index.

For simplicity the more general term “effective refractive index” or“effective index” will often be used herein, regardless of whether theregion of the fiber under discussion is substantially homogeneous(defined below), includes features arranged such that the geometricalindex is a useful concept, or includes features arranged so as toprovide a selected photonic bandgap wherein a selected range ofwavelengths is effectively prohibited from propagating in a selectedmanner in a region (e.g., a cladding). To provide a selected photonicbandgap, the features are typically smaller and/or more closely spacedthan in the “geometrical index” case.

The term “substantially homogeneous” as used herein to refer to a regionof a fiber, means that the region is not considered to have featuresthat provide, in terms of light guidance at wavelengths of operation ofa fiber, a meaningful photonic bandgap or a meaningful geometrical indexof refraction. By way of example and not limitation, the term is meantto include conventional doped or undoped host materials, such as, forexample, an undoped silica host or a silica host doped with typicaldopants (e.g., germanium, fluorine, boron, phosphorus, one or more rareearths) that raise, lower or leave substantially unaffected the index ofrefraction of the host material at wavelengths of operation. Asubstantially homogeneous region need not have a constant index ofrefraction throughout the region. For example, the graded index core ofa conventional graded index fiber can be considered to be substantiallyhomogeneous, although the refractive index can vary across at least partof the core.

The term “layer”, as used herein, does not require that a layer beformed in a particular manner or have a particular thickness orcomposition; for example, one region can be formed over and subsequentto another substantially identical region and the two regions could beconsidered to form a single layer. The proper emphasis is on theintended functional characteristic(s) of a layer.

The different concepts and structures described above are typicallyalike in at least one aspect: regardless of whether a region (e.g., acladding) of a fiber is substantially homogeneous, includes featureshaving a large volume fraction such that the concept of geometric indexis relevant, or provides a photonic bandgap, typically the region isdisposed about another region (e.g., core) and has an effective index ofrefraction that is selected to be less than the effective index ofrefraction of the other region (the core) so as to tend to confine lightto the region (the core) to facilitate the guidance of light thereby.

In certain embodiments of the invention an optical fiber, such as acladding pumped optical fiber, comprises a core, a pump claddingdisposed about the core, and a second cladding disposed about the pumpcladding, wherein the second cladding includes an arrangement offeatures and surrounding material so as to provide a selected photonicbandgap for tending to confine pump light within the inner cladding

Terms are used herein as understood by one of ordinary skill in the art,and definitions provided herein are as understood by one of ordinaryskill in the art. For example, as used herein the term “optical”, suchas is used in the term “optical waveguide” or “optical fiber”, is usedto mean a waveguide or fiber, as the case may be, for use withelectromagnetic energy, as is well understood by those of ordinary skillin the art. It is inappropriate for the term “optical” (or for the term“light”), as used herein, to be limited to the range of visiblewavelengths, as is readily appreciated by one of ordinary skill, butperhaps not appreciated by one not of ordinary skill inclined toinappropriately rely solely on a layman's dictionary, which may restrictthe terms “optical” or “light” to visible wavelengths.

Several features of the invention are described above and elsewhereherein. Not every specific combination of features according to whichthe invention can be practiced is explicitly enumerated herein. Ingeneral, it is understood by one of ordinary skill in the art thatfeatures described in conjunction with one embodiment can be included inany other embodiment described herein, excepting of course combinationsof features that are mutually exclusive.

Further advantages, novel features, and objects of the invention willbecome apparent from the following detailed description of non-limitingembodiments of the invention when considered in conjunction with theaccompanying FIGURES. For purposes of clarity, not every component islabeled in every one of the following FIGURES, nor is every component ofeach embodiment of the invention shown where illustration is notconsidered necessary to allow those of ordinary skill in the art tounderstand the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a cross section of an optical fiberarticle according to one embodiment of the present invention;

FIG. 2 schematically illustrates one embodiment of an apparatus forproviding the optical fiber article of FIG. 1;

FIG. 3 schematically illustrates another embodiment of an apparatus forproviding the optical fiber article of FIG. 1;

FIG. 4A schematically illustrates a sheet material that can be used toform one example of the second preform of FIG. 2 or FIG. 3;

FIG. 4B is a cross section, taken in a plane perpendicular to thelongitudinal axis of the of the optical fiber 14, of a second preform 52of FIGS. 2 and 3, that can be formed from the sheet material of FIG. 4A;

FIG. 5A schematically illustrates a second example of a sheet materialthat can be used to form a second example of the second preform of FIG.2 or FIG. 3;

FIG. 5B is a cross section of a second preform that can be formed by thesecond sheet material of FIG. 5A;

FIG. 6 illustrates a third example of a sheet material that can be usedto form a third example of the second preform of FIG. 2 or FIG. 3;

FIG. 7A schematically illustrates another embodiment of an optical fiberarticle according to the present invention;

FIG. 7B schematically illustrates an additional embodiment of an opticalfiber article according to the present invention; and

FIG. 7C schematically illustrates a further embodiment of an opticalfiber article according to the present invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a cross section of an optical fiberarticle 12 according to one embodiment of the present invention. Thecross section shown in FIG. 1 is taken perpendicular to the longitudinalaxis of the optical fiber article 12. The optical fiber article 12 caninclude an optical fiber 14, which can include at least a core, and aregion 16 disposed about the optical fiber 14. The region 16 can contactthe core of the optical fiber 14. The region 16 can protect the opticalfiber 14, and/or can provide an optical cladding for the optical fiber14. In some practices of the invention, the optical fiber 14 can includean optical cladding (e.g., a transparent glass cladding) disposed aboutthe core as well as one or more protective coatings (e.g., acrylatepolymer coatings) disposed about the cladding and/or the core, and theregion 16 is disposed about the optical cladding and/or the protectivecoatings of the optical fiber 14. In one embodiment of the invention,the optical fiber 14 can include a glass core and an optical glasscladding disposed about the core, and the region 16 can comprise apolymer, such as polyimide, for protecting the optical fiber 14. Theregion 16 can provide a hermetic seal for the optical fiber 14. Theregion 16 can comprise a metal, such as by, for example, comprising ametal and a polymer.

The region 16 can be substantially homogeneous. The region 16 can beinhomogeneous and can comprise, for example, discrete regions ofdifferent compositions and/or optical properties at a wavelength ofinterest, such as, for example, a wavelength at which the optical fiberarticle is intended to propagate or guide electromagnetic energy. Forexample, the region 16 can comprises concentric rings or annuli, wherethe composition of one annulus or ring can be different than thecomposition of another annulus or ring.

FIG. 2 schematically illustrates one embodiment of an apparatus 20 forproviding the optical fiber article 12 of FIG. 1. The heater 28, whichcan comprise a graphite furnace, heats one end of the optical fiberpreform 32 to facilitate the drawing of the optical fiber 14 from theoptical fiber preform 32. The apparatus 20 can include a device 38 formeasuring the diameter of the optical fiber 14. The apparatus 20 canalso include a device 42 (e.g., one or more “coating cups” includingdies) for disposing one or more coatings (e.g., soft and hard acrylatepolymer coatings known in the art) about the optical fiber 14. Theapparatus 20 can also include a device (e.g., one or more ultravioletlamps) for curing, at least in part, the coatings disposed about theoptical fiber 14 by the device 38.

The apparatus 20 can include a second heater 50 for heating a secondpreform 52 for drawing the preform so as to dispose the region 16 aboutthe optical fiber 14, where the region 16 is derived, at least in part,from the second preform 52. The second preform 52 can define theaperture 54, and the optical fiber 14 can pass through the aperture 54for facilitating drawing the second preform 52 for disposing the region16 about the optical fiber 14 so as to form the optical fiber article12. The second preform 52 can comprise one or more of a polymer, ametal, or any other suitable material, alone or in combination.

The apparatus 20 can also include a device 64 (e.g., a delivery tube)for providing an adhesion promoter (e.g., a silane) for promotingadhesion of the region 16 to the optical fiber 14. The device 64 candeliver the adhesion promoter to or near the aperture 54. The opticalfiber article 12 can be wound about drum, or spool, 60. Fiber vendorsusually supply fiber so spooled. The apparatus 20 can include provisionfor drawing a selected degree of vacuum on the interior of the secondpreform 52. Such provision can include a feedthrough tube 68 in fluidcommunication with the interior of the second preform 52 and a sealingdevice 70 for sealing off the interior of the preform 52 so as tofacilitate the drawing of the selected degree of vacuum, as indicatedschematically in FIG. 2. The feedthrough tube 68 can be in fluidcommunication with a vacuum pump (not shown).

Typically, the apparatus 20 can be arranged on a tower. Draw towers fordrawing conventional optical fibers from an optical fiber preform arewell known in the art. The apparatus 20 can include other devices, suchas a device for measuring the concentricity of the coatings disposedabout the optical fiber 14 by the device 38, and/or a device formeasuring the concentricity of the region 16 drawn from the secondpreform 52. Various drawing parameters (e.g., temperature of one or bothof the heaters 28 and 50, the draw speed, the draw tension, etc.) can becontrolled responsive to information provided by one or more measurementdevices, such as the device 38 for determining the diameter of theoptical fiber 14, so as to provide the optical fiber 14 and/or theoptical fiber article 12 with desired properties.

Note that one or more of the devices 38, 40 and 42 can be disposed“downstream” of the second preform 52, as indicated schematically by thearrow 72, rather than “upstream”, as shown in FIG. 2. In this instance,any coatings added by the coating device 40 will be disposed over theregion 16, rather than the region 16 being disposed over one or morecoatings added by the coating device 40. Of course, it is within thescope of the invention to add coatings that can form layers bothupstream and downstream of the second preform 52.

As schematically illustrated in FIG. 3, in one embodiment of theinvention, the second preform 52 can be located adjacent the heater 28such that residual heat from the drawing of the optical fiber 14 fromthe preform 32 can contribute to or be solely responsible for supplyingthe heat for drawing the second preform 52 so as to dispose the region16 about the optical fiber 14. Some of all of the heat can be carried bythe optical fiber 14 as it leaves the region of the heater 28.

As shown in FIGS. 2 and 3, fabrication of the optical fiber 14 can besubstantially contemporaneous with the disposing of the region 16 aboutthe optical fiber 14 to form the optical fiber article 12 (e.g., drawingof the second preform 52 can occur on the same tower as the formation ofthe optical fiber, such as by draw, and/or can occur with the opticalfiber 14 not having been previously spooled). “Substantiallycontemporaneous”, as used in this context, is not to mean that thedrawing of the second preform 52 cannot be subsequent to providing theoptical fiber 14. Alternatively, the optical fiber 14 can be pre-madeand hence simply be provided to the second preform 52 from a storagespool. The optical fiber 14 can be fabricated by any suitable method orcombinations thereof, such as, for example, drawing the fiber from apreform, extruding the fiber, or forming the fiber using one or morecrucibles, such as the dual nested crucible method well known in theart. Note that although FIGS. 2 and 3 show an optical fiber preform 32that is separated from the second preform 52, in certain circumstancesthe second preform 52 could be disposed about the optical fiber preform32 to form a composite preform that is then drawn to form the opticalfiber article 12.

FIG. 4A schematically illustrates a sheet material 80 that can be usedto form one example of the second preform 52. The preform 52 cancomprise a spiral 84 of the sheet material 80, and the sheet materialcan be rolled to form the spiral 84 and to define the aperture 54, asillustrated in FIG. 4B. The spiral 84 can be secured to reduce thetendency of the spiral 84 to unravel. The spiral 84 can be fused, suchas by causing heating of all or a portion of the spiral 84, prior todrawing the preform 52 to dispose the region 16 about the optical fiber14. The sheet material can comprise a polymer (e.g., apolyethersulfone). The sheet material can comprise a polyimide, such as,for example, Kapton™ or Cirlex™, both of which are available fromDuPont. Polyimide tubing is available from Furukawa Electric.

FIG. 5B schematically illustrates a cross section of another example ofa second preform 52, wherein the second preform 52 comprises first andsecond spirals, 94 and 96 respectively. The first spiral 94 can be woundfrom a first sheet material and the second spiral 96 can be wound from asecond sheet material. The first and second sheet materials can berolled together such that the first spiral 94 is inside of the secondspiral 96, as shown in FIG. 5B. The first and second sheet materials canhave substantially the same composition, or can have differentcompositions and can have different optical properties, such asdifferent refractive indices. For example, the first sheet material cancomprises a metal and the second sheet material can comprise a polymer,such as a polyimide. The region 16 will accordingly include first andsecond spirals corresponding at least in part to the first and secondspirals of the preform from which the region 16 is drawn. The first andsecond spirals can be formed from a sheet material 100 shown in FIG. 5A,wherein the sheet material 100 comprises a first layer or sheet region104 adhering to a second layer or sheet region 106, and the first sheetregion 104 forms spiral 94 and the second sheet region 106 forms spiral96. The first and second sheet regions 104 and 106 can comprisedifferent compositions.

In one embodiment of the invention, a preform, and hence the region 16,comprises at least three spirals, where two of the spirals areelectrically conductive (i.e., are not insulating). A conductive spiralcan consist of or comprise metals (e.g., a metalloid polymer), and arepreferably electrically insulated from each other by another of thespirals, such as a polymer spiral, interposed between the two conductivespirals. Such a configuration may be useful in an optical fiber forpower or signal delivery. See, for example, FIG. 6, which schematicallyillustrates an example of a sheet material 150 that can be rolled toprovide a preform having such spirals, where the preform can then bedrawn to provide a region 16 having such spirals. The sheet material 150comprises insulating polymer layers 154A and 154B and conductive layers156A and 156B.

FIG. 7A schematically illustrates a cross section of another embodimentof an optical fiber article 212 according to the present invention. Theoptical fiber article 212 can have a longitudinal axis, and the crosssectional view of the optical fiber article 212 presented in FIG. 7A canbe taken perpendicular to the longitudinal axis. The optical fiberarticle 212 comprises a core 214, a first or inner cladding 217 disposedabout the core and a second or outer cladding 219 disposed about thefirst cladding 217. The optical fiber article 212 can also include anouter region 221 disposed about the second cladding 219. The outerregion 221 can provide mechanical strength. The outer region 221 can bederived from a glass tube, such as, for example, a silica glass tubetypically used in making an optical fiber preform.

The core 214 can include one or more selected rare earths (atomicnumbers 57-71) for absorbing selected wavelengths of light. In certainembodiments of the invention, the rare earth can provide light having asecond or signal wavelength responsive to absorbing light (i.e., pumplight) having a first or pump wavelength that is different (e.g.,shorter) than the first wavelength. The rare earth is typically added asdopant to a host material, such as a host material of silica glass. Anoptical fiber article comprising a rare earth can form the basis of anoptical fiber laser, optical fiber amplifier or superfluorescent source,for example, as is known in the art. Rare earths understood to beparticularly of interested for fiber lasers, amplifiers and the like,can be one or more of erbium, ytterbium, thulium, and neodymium. Opticalfiber articles comprising both erbium and ytterbium are known to beuseful in certain applications, such as, for example, a laser oramplifier operating at an “eye safe” wavelength.

The first or inner cladding 217 can act as a pump cladding for receivingpump radiation for absorption of the pump light by the one or more rareearths comprised by the optical fiber article 212. Typically, one orboth of the core 214 and the inner cladding 217 can comprise a rareearth. The inner cladding 217 can have an effective index of refractionthat is less than the effective index of refraction of the core 214, andthe second cladding 219 can have an effective index of refraction thatis less than the effective index of refraction of the inner cladding217.

The inner cladding 217 can have a relatively high cross sectional areaand a rather high numerical aperture (NA) for increased capture of lightfrom a pump light source having a high numerical aperture, and canfacilitate delivery of such pump light to the one or more rare earthsfor absorption thereby. In one embodiment of the invention the innercladding 217 can tend to confine light having a selected wavelength(e.g., the first or signal wavelength) to the core 214, but does nottend to so confine the light having the selected wavelength via aphotonic bandgap effect, whereas the second cladding 219 provides aselected photonic bandgap for confining light (e.g., light having thesecond or pump wavelength) to a region about which the second claddingis disposed (e.g., the inner cladding 217 or an additional claddinginterposed between the inner cladding and the second cladding). Forexample, the inner cladding 217 can be substantially homogeneous, andcan consist essentially of silica glass or doped silica glass, or theinner cladding 217 can comprise features so as to confine light to thecore 214 based on the geometrical index effect. For example, the innercladding can comprise a plurality of isolated features 225, where eachisolated feature includes an optical property (e.g., index ofrefraction) that is different than material adjacent the features (e.g.,material of the cladding 217 surrounding each of the features) forproviding said pump cladding with a selected geometric refractive index.The term “isolated”, as used herein with reference to features isintended to distinguish the features from regions that substantiallysurround the core, such as the layers 231 and 233 comprised by thesecond cladding 219, described in more detail below.

In another embodiment of the invention, the inner cladding 217 isadapted to provide a selected photonic bandgap for tending to confinelight having a selected wavelength to a region about which the innercladding 217 is disposed (e.g., the core 214).

The second cladding 219 can have an inner perimeter 227. The secondcladding 219 can comprise a plurality of layers 229 for providing theselected photonic bandgap. The plurality of layers 229 can include afirst layer (e.g., one of the layers 231) having a different opticalproperty than a second layer (e.g., one of the layers 233). For example,the layers 231 can each have a higher index of refraction than thelayers 233. For example, layers 231 can have a lower index of refractionthan layers 233. The layers 231 and 233 can alternate, as shown in FIG.7A. The layers 231 and 233 can be adapted to provide a photonic bandgapselected for tending to confine light, such as, for example, pump light,within the inner perimeter 227 of the second cladding 219. As shown inFIG. 7A, the plurality of layers 229 can comprise a plurality ofconcentric closed rings (“closed” means that the ring closes on itselfso there is no free end), where each of the layers 231 and 233 forms aclosed ring and is concentric with the other layers.

It is known in the art that a selected region (i.e., the second cladding219) can include an arrangement of layers of higher and lower index ofrefraction so as to provide a photonic bandgap that can tend to confinelight to a region (i.e., a core, which can comprise air) about which theselected region is disposed. See the work of Yoel Fink of theMassachusetts Institute of Technology, Cambridge, Mass., USA (MIT),typically in conjunction with others, such as, for example, JohnJoannopoulos, also of MIT, and from the work of OmniGuide Inc., OneKendall Square, Building 100, Third Floor, Cambridge, Mass., 02139, USA(OmniGuide). See, in general, other patents, patent applications andpublications of which Yoel Fink or John Joannopoulos is an inventor orauthor or that are associated with OmniGuide Inc. See, for example, U.S.Pat. No. 6,130,780, entitled “High Omnidirectional Reflector”, issued onOct. 10, 2000 to inventors Joannopoulos, Fan, Winn and Fink, andassigned at the time of issue to MIT. More particularly, see U.S. Pat.No. 6,463,200, entitled “Omnidirectional Multilayer Device for EnhancedOptical Waveguiding”, issued on Oct. 8, 2002 to inventors Fink, Fan,Thomas, Chen and Joannopoulos and assigned at the time of issue to MIT(the '200 patent). The arrangement of layers can form a dielectricmirror.

The arrangement of layers can include closed concentric cylinders orrings with alternating indices of refraction n₁, n₂ that surround thecore of dielectric material no, such as air. See, for example, FIG. 6Aof the '200 patent and the accompanying discussion of FIG. 6A. Adjacentlayers can have different thicknesses. Note that an exemplary embodimentof the '200 patent would involve each layer consisting of differentmaterial and corresponding different layer thickness, and the parametersof the multilayer film can be chosen such that light from any relevantincident angle and relevant polarization is completely reflected by thearrangement of layers for a selected range of signal frequencies.

The arrangement of layers can include at least one layer that iscontinuous and that forms a spiral when viewed in cross section. See,for example, PCT Patent Application PCT/U.S. 2003/039344, entitled “HighPower, Low-Loss Fiber Waveguide” and published in English as WO2004/052078 A2 on Jun. 24, 2004 in the names of inventors Benoit, Fink,Joannopoulos, Hart and Temelkuran. Such an arrangement of layers can bedrawn from a preform that includes a spiral, and such a preform can beformed from a suitable sheet material, as taught in the foregoingpublished PCT Patent Application. Accordingly, in one embodiment of theinvention, the plurality of layers 229 can include at least a firstlayer that forms a spiral about the longitudinal axis. Typically, theplurality of layers 229 will include two layers that spiral about thelongitudinal axis, where one of the layers spirals inside the other ofthe layers. The plurality of layers can appear as the spiral of layers94 and 96 shown in FIG. 5B.

It is not necessary to use an arrangement of layers to provide a regionof an optical fiber with a selected photonic bandgap. A region canprovide a selected photonic bandgap by including appropriately designedlongitudinally extending features (e.g., voids) in an appropriate hostmaterial (e.g., silica glass). See, for example, papers, patents andpatent applications in the names of one or more of Timothy Birks,Phillip Russell and Jes Broeng. More particularly, see published PCTPatent Application PCT/GB98/01782, entitled “Single Mode Optical Fibre”and published in English as WO 99/00685 on Jan. 7, 1999 in the names ofinventors Birks, Knight and Russell; published PCT Patent ApplicationPCT/DK99/00193, entitled “A Photonic Band Gap Fibre” and published inEnglish as WO 99/64904 on Dec. 16, 1999 in the names of inventorsBroeng, Barkou, and Bjarklev; published PCT Patent Application PCTDK/99/00279, entitled “Microstructured Optical Fibres” and published inEnglish as WO 99/64903 on Dec. 16, 1999 in the names of inventorsBroeng, Barkou and Bjarklev; and published PCT Patent ApplicationPCT/GB00/04744, entitled “Improvements in or Relating to PhotonicCrystal Fibres” and published in English as WO 01/42829 on Jun. 14, 2001in the names of inventors Russell, Birks, Knight and Mangan. See alsoU.S. Patent Application U.S. 2003/0165313, entitled “Optical Fibre withHigh Numerical Aperture, Method of its Production, and Use Thereof”,published Sep. 4, 2003 in the names of inventors Broeng, Bjarklev,Libori, Folkenberg and Vienne.

Accordingly, see FIG. 7B, which schematically illustrates anotherembodiment of the present invention. The optical fiber article 312 caninclude a core 314, an inner cladding 317 disposed about the core 314,and a second cladding 319 disposed about the inner cladding 317. Theoptical fiber article 312 can conform to the description of the opticalfiber article 212 above in conjunction with FIG. 7A, except that thesecond cladding 319 comprises a plurality of isolated features 323having an optical property (e.g., index of refraction) that is differentthan the material adjacent the features 323 for providing the selectedphotonic bandgap for tending to confine light having a selectedwavelength to a region (e.g., the inner cladding 317) about which thesecond cladding 319 is disposed. The isolated features 323 can extendlongitudinally, and can comprise longitudinally extending voids.

FIG. 7C illustrates another embodiment of an optical fiber articleaccording to the present invention. The optical fiber article 412comprises a core 414, and inner cladding 417 disposed about the core414, which inner cladding 417 can be a pump cladding, a second cladding419 disposed about the inner cladding 417, and an additional cladding435 disposed about the inner cladding and about which the secondcladding 419 is disposed. The additional cladding 435 can comprise aneffective index of refraction that is less than the effective index ofrefraction of the inner cladding 417. The inner cladding 417 can besubstantially homogeneous.

The additional cladding 435 can comprise a plurality of isolatedfeatures 443, where each of the features has an optical property (e.g.,index of refraction) that is different than material adjacent thefeature for providing said additional cladding with a selected geometricrefractive index (or a selected photonic bandgap) for tending to confinepump light to the inner cladding 417. The plurality of isolated features443 can comprise a plurality of longitudinally extending voids. Thedescription of the various aspects of the optical fiber articles 212 and312 can apply to the optical fiber 412 as well, and the description isnot repeated in the same detail here. The second cladding can provide aselected photonic bandgap for tending to confine light (e.g., pumplight) to a region about which the second cladding 419 is disposed(e.g., the additional cladding 435).

The second cladding 419 can include a plurality of layers 429 includinga first layer 431 having a different optical property than a secondlayer 433 for providing the photonic bandgap, as, for example, isdescribed in conjunction with the layers of FIG. 7A. The first layer 431can have a higher index of refraction than the second layer 433. Theplurality of layers 429 can include alternating layers of different,such as high and low, refractive indices. The plurality of layers cancomprise a plurality of concentric closed rings, as shown in FIG. 7C, orcan comprise one or more layers that form one or more spirals, as notedabove in conjunction with the discussion of FIGS. 7A and 7B. The opticalfiber article 412 can include a region 421 disposed about the core,inner, second and additional claddings for providing structural support.A region (e.g., the second cladding) of the optical fiber article 412can include a plurality of isolated features, such as longitudinallyextending voids, which voids can comprise air, for contributing toprovision of the photonic bandgap of the second cladding. The secondcladding 419 can include the isolated features in addition to, or inlieu of, the plurality of layers 429.

A region of a fiber according to the invention can include one or moreelements or materials. Such elements or materials can be, for example,included as dopants in a host or background material. For example, it iswell known in the art to raise the index of refraction of silica bydoping the silica with germanium. One of ordinary skill in the artunderstands that a material or element can be combined with orincorporated into another material, such as a host material, accordingto a chemical formulation that depends on materials in question and/oron processing parameters. For example, when the host material is silicaglass, most of the germanium is understood to be typically incorporatedas germania or GeO₂. Similarly, it is understood that boron is typicallyincorporated as B₂O₃. However, the invention is not limited to glasshosts or silica glass hosts, and can be practiced with other types ofmaterials as host, such as plastics or other types of glasses, such aschalcogenide glasses or fluoride or phosphate glasses, wherein germaniumor other elements are incorporated into different compounds than thosespecifically noted above. Stating that a fiber includes a material, suchas boron, for example, means that the material is included in some formin the fiber, where it is understood that the form can be different,depending on the circumstances.

Those skilled in the art will recognize or be able to ascertain using nomore than routine experimentation many equivalents to the specificembodiments of the invention described herein. It is therefore to beunderstood that the foregoing embodiments are presented by way ofexample only and that within the scope of the appended claims andequivalents thereto, the invention may be practiced otherwise than asspecifically described. The present invention is directed to eachindividual feature, system, material and/or method described herein. Inaddition, any combination of two or more such features, systems,materials and/or methods, if such features, systems, materials and/ormethods are not expressly taught as mutually inconsistent, is includedwithin the scope of the present invention.

In the claims as well as in the specification above all transitionalphrases such as “comprising”, “including”, “carrying”, “having”,“containing”, “involving” and the like are understood to be open-ended.Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the U.S. Patent Office Manual of PatentExamining Procedure §2111.03, 7th Edition, Revision.

1. A method of making an optical fiber article, comprising: providing anoptical fiber comprising at least a core; providing a preform; andsubsequent to the foregoing providing of the optical fiber and thepreform, drawing the preform so as to dispose a region about the opticalfiber.
 2. The method of claim 1 wherein the preform comprises a firstpolymer.
 3. The method of claim 2 wherein the first polymer comprises apolyimide.
 4. The method of claim 2 wherein the region comprises asecond polymer.
 5. The method of claim 4 wherein the second polymer issubstantially identical to the first polymer.
 6. The method of claim 1wherein the preform comprises a metal.
 7. The method of claim 1 whereinthe preform comprises a first metal and a first polymer and wherein theregion comprises a second metal and a second polymer.
 8. The method ofclaim 1 wherein the preform defines an aperture and wherein drawing thepreform comprises passing the optical fiber through the aperture.
 9. Themethod of claim 1 wherein providing the preform comprises providing asheet material and forming the sheet material into a tube.
 10. Themethod of claim 9 wherein providing the preform comprises fusingadjacent portions of the tube together.
 11. The method of claim 9wherein the tube comprises a spiral of the sheet material.
 12. Themethod of claim 9 wherein the sheet material includes a layer of a firstmaterial adhered to a layer of a second material that is different thanthe first material.
 13. The method of claim 12 wherein the firstmaterial comprises a metal and the second material comprises a polymer.14. The method of claim 1 wherein providing the fiber comprises drawingthe fiber from an optical fiber preform.
 15. The method of claim 14wherein drawing the fiber and drawing the preform to dispose the regionabout the optical fiber occur substantially contemporaneously.
 16. Themethod of claim 1 wherein providing the optical fiber includesrefraining from disposing a polymer protective region about the opticalfiber.
 17. The method of claim 1 comprising providing an adhesionpromoter while drawing the preform for promoting adhesion of the regionto the fiber.
 18. The method of claim 17 wherein the adhesion promotercomprises a silane.